One type of electric motor is a brushless motor such as, but not limited to, a switched-reluctance motor. One example of a conventional switched-reluctance motor has 8 stator poles and 6 rotor poles. This motor example has 4 motor phases (i.e., the number of stator poles divided by two) which are the four opposite pairs of stator poles. This motor example has a machine step of 60 degrees (i.e., 360 degrees divided by the number of rotor poles) which is the rotor period, in degrees, between a rotor pole being aligned with a first stator pole (assume the rotor-position angle is minus 60 degrees) and that rotor pole rotating and being aligned with an adjacent second stator pole (where the rotor-position angle is 0 degrees). The unaligned rotor-position angle is midway between the two aligned rotor-position angles and therefore is minus 30 degrees. The inductance is at a peak (which may be a flat peak) at a rotor-position angle of minus 60 degrees, then fails to a valley (which may be a flat valley) at a rotor-position angle of minus 30 degrees and then rises to the peak at a rotor-position angle of 0 degrees.
One conventional application of a switched-reluctance motor is to operate the motor only in the first quadrant of positive motor torque and positive motor speed (i.e., in a forward motoring mode) where the first quadrant is a quadrant of the motor torque versus motor speed diagram. Another conventional application is to operate the motor only in the second quadrant of negative torque and positive motor speed (i.e., in a regenerative braking or a generator mode). A conventional method for controlling a switched-reluctance motor is to choose current turn-on and turn-off rotor-position angles to maximize machine efficiency. In one conventional implementation, when the motor is operating in the first quadrant, the current turn-on rotor-position angle is chosen at the beginning of the rising inductance region (e.g., at a rotor-position angle of minus 29 degrees in the previous motor example). A further conventional application is to operate the motor in all four quadrants wherein the motor is controlled for constant power in the second and fourth quadrants.
What is needed is improved control of an electric motor useful, for example and without limitation, in a system including a brake caliper operatively connected to the motor.